1. Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education Department of Chemistry Tsinghua University Beijing 100084 P. R. China
2. School of Materials Science & Engineering Tianjin Key Laboratory of Molecular Optoelectronic Sciences Tianjin University Tianjin 300072 P. R. China
3. Visionox Technology Inc Jiangsu 215300 P. R. China
4. Laboratory of Flexible Electronics Technology Tsinghua University Beijing 100084 P. R. China